Antennas incorporated for radio wave radiation in handy-type compact radio communication equipment, movable units of cordless telephone sets, etc. include a telescopic rod antenna which is used from the point of view of portability, transportation and storage, and a flexible antenna which is used from the point of view of protection of the antenna body against damage.
FIGS. 3 and 4 show a radiotelephone equipped with a conventional flexible antenna which can be received in a body of the radiotelephone. In this figure, numeral 31 is a flexible antenna having an internal spiral conductor 32, numeral 34 is a stopper provided at the base of the flexible antenna, and numeral 35 is a bearing provided within a cabinet 38 for slidably holding the flexible antenna 31. Thus, the flexible antenna 31 is slidably supported by the bearing 35 and is protected by the stopper 34 against removal from the cabinet 38. Numeral 36 is an electrode strip provided on the base of the flexible antenna 31. The electrode strip 36 and the internal spiral conductor 32 are held in conduction with each other. Numeral 37 is an electrode strip secured to the bearing 35. When the flexible antenna 31 is pulled out as shown in FIG. 3, the electrode strip 36 and the electrode strip 37 contact with each other, thereby electrically connecting the spiral conductor 32 and transmitter and receiver circuits (not shown).
In the unused condition, the flexible antenna 31 is received within the cabinet 38, as shown in FIG. 4. In use, the user pulls out the flexible antenna 31 from the cabinet 38 while gripping the front end of the flexible antenna 31. When the flexible antenna 31 is fully extended, the electrode strip 36 on the flexible antenna side is brought into contact with the electrode strip 37 secured to the bearing 35, whereupon the transmitter and receiver circuits and the spiral conductor 32 are electrically connected with each other.
With this construction, transmission and reception of a message is not possible until the flexible antenna 31 is fully pulled out from the cabinet, as shown in FIG. 3.
In some instances, however, it is desired that a receiver function is kept alive even when the antenna is received in the cabinet. This is because it is very convenient for the user if the radiotelephone has a construction enabling such a manner of use that the radiotelephone is held compactly in a pocket or the like of the user while keeping the receiver function in an activated condition, and when a call signal is received, the user draws the radio-telephone from the pocket and pulls out the antenna from the cabinet for commencing transmission of a message. To realize this manner of use, however, a receive-only sub-antenna which is operable in the received condition must be provided within the cabinet in addition to the main antenna. Furthermore, in order to connect the transmitter and receiver circuits selectively with the main antenna and the sub-antenna depending on the position of the main antenna, a switching means must be provided. Thus, the above-mentioned arrangement increases the number of structural components of the radiotelephone.
Furthermore, when the antenna of the construction shown in FIG. 3 is depressed during transmission of a message, connection between the antenna and the transmitter circuit is interrupted for a moment. In this instance, the impedance and the resonance frequency of the antenna side as viewed from the transmitter circuit change greatly. If such a great change in impedance and resonance frequency occurs during the transmission of a message, the transmitter circuit may be damaged.
The currents flowing between the transmitter circuit and the main antenna and also between the transmitter circuit and the sub-antenna are high-frequency currents in a radio frequency band. Contacts of the switching means must be disposed at portions through which the high-frequency currents flow. In order to minimize a high-frequency current loss, an expensive switching means is needed, which will increase the manufacturing cost of the radiotelephone.